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  • Is my Calculation True for 60 Watt Off-Grid Lighthing ?

    I want to desing 60 W off grid lighting for my garden in los angeles. and It is going to light all the night (11 hours) is my calculation true ?

    Consumption = 60 Watt x 11 hours x 1.25 (safety factor) = 825 Watt.hours

    I looked at the average solar radiation data from gaisma, average sun hour for los angeles is about 4,2 hours

    Size of Panel =( 825 Watt.hours/ 4.2 hours) = 196,42 --> 200 Watt panel

    all losses =0,85
    Dept of Discharge = 0,5
    3 days reserve

    Size of the Battery= 825 Watt.hours / (0,85 x 0,5 x 12 Volt ) x 3 days = 485 AH Battery ---> 2 x 242 AH battery 12 Volt

    Size of Controller = (200 Watts / 12V) X 1.2 (Safety factor) = 20 A solar controller


    If I use 2 x 100 Watts solar panel for desinging 24 Volt system is it better ?


    Thank you.

  • #2
    Originally posted by malborn View Post
    I want to desing 60 W off grid lighting for my garden in los angeles. and It is going to light all the night (11 hours) is my calculation true ?

    Consumption = 60 Watt x 11 hours x 1.25 (safety factor) = 825 Watt.hours
    Incorrect but you are on the right track.

    Where you went wrong is with your correction factor [CF] of 1.25. The CF depends on what type of Charge Controller you use. If you intend to go the very expensive route and use a PWM controller CF = 2. If you go the least expensive route and use MPPT CF = 1.5. It will take you a while to figure out why MPPT is less expensive. MPPT controllers are roughly 5 times more expensive.

    So assuming you use MPPT Panel Wattage = [60 watts x 11 hours x 1.5] 4.2 hours = 235 watts. So you buy a single 250 watt GT panel and a 20 amp MPPT controller Should cost you around $500. Don't go cheap on Charge Controllers. A good 20 amp unit is $200

    For PWM you would need [60 x 11 x 2] /4.2 = 315 watts. That required 3 110 watt Battery panels and a 20 amp PWM controler. That will cost you $700.

    Last part is the battery. Assuming 12 volt system will require [60 x 11 x 5] / 12 volts = 275 AH. That will be 2 6-volt 275 AH battery. A decent 3 to 4 year battery will cost you roughly $400 every 3 or 4 years. An excellent choice would be a pair of Trojan T-145's
    MSEE, PE

    Comment


    • #3
      I looked at the average solar radiation data from gaisma, average sun hour for los angeles is about 4,2 hours
      Is that the yearly average, or the winter time average? You need to use the Winter (shortest sun month) as your design start point. (or whatever month is the shortest month you will be using loads, maybe you don't use garden lights in Dec)
      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister

      Comment


      • #4
        Originally posted by Sunking View Post
        Incorrect but you are on the right track.

        Where you went wrong is with your correction factor [CF] of 1.25. The CF depends on what type of Charge Controller you use. If you intend to go the very expensive route and use a PWM controller CF = 2. If you go the least expensive route and use MPPT CF = 1.5. It will take you a while to figure out why MPPT is less expensive. MPPT controllers are roughly 5 times more expensive.

        So assuming you use MPPT Panel Wattage = [60 watts x 11 hours x 1.5] 4.2 hours = 235 watts. So you buy a single 250 watt GT panel and a 20 amp MPPT controller Should cost you around $500. Don't go cheap on Charge Controllers. A good 20 amp unit is $200

        For PWM you would need [60 x 11 x 2] /4.2 = 315 watts. That required 3 110 watt Battery panels and a 20 amp PWM controler. That will cost you $700.

        Last part is the battery. Assuming 12 volt system will require [60 x 11 x 5] / 12 volts = 275 AH. That will be 2 6-volt 275 AH battery. A decent 3 to 4 year battery will cost you roughly $400 every 3 or 4 years. An excellent choice would be a pair of Trojan T-145's
        Thank you for useful reply
        I have two question:
        Could you explain please what is "5" in [60 x 11 x 5] / 12 volts = 275 AH formula ? I want 3 days reserve.

        Could I use 2 X 12 Volt battery in paralel 275AH/2 = 137.5 AH ?

        Thank you

        Comment


        • #5
          Originally posted by malborn View Post
          Thank you for useful reply
          I have two question:
          Could you explain please what is "5" in [60 x 11 x 5] / 12 volts = 275 AH formula ? I want 3 days reserve.

          Could I use 2 X 12 Volt battery in paralel 275AH/2 = 137.5 AH ?

          Thank you
          You should never use more than 20% of the battery in a day. So multiplying by 5 is the same as dividing by 20%. That also gives you 2.5 days autonomy before hitting the 50% SOC that you should never go below. If you still desire to have 3 days than substitute 6 instead of 5.

          You could use 2 12v batteries in parallel but would be better off to use 2 6v in series.

          WWW

          Comment


          • #6
            Originally posted by malborn View Post
            Thank you for useful reply
            I have two question:
            Could you explain please what is "5" in [60 x 11 x 5] / 12 volts = 275 AH formula ? I want 3 days reserve.

            Could I use 2 X 12 Volt battery in paralel 275AH/2 = 137.5 AH ?

            Thank you
            WWW answered the why to use 5 days (2.5 usable). Never ever parallel batteries unless necessary. Parallel batteries wil just shorten cycle life. It is never necessary to parallel batteries. Get out the 12 volt box. Lead acid batteries are 2 volts, not 12.

            EDIT: As Mike noted you DO NOT use average Sun Hours for Off-Grid, or you go dark in the winter. Use worse case.
            MSEE, PE

            Comment


            • #7
              Thank you very much for helping me. your answers are so useful

              Comment


              • #8
                In order to make it cheaper by using less solar controller amphere. should I desing it at 24 V ?
                and can I do that by connecting two 12 solar panel in series and connecting 12 volt batteries in series ?
                Is there anything else that I aware of ?

                Thank you.

                Comment


                • #9
                  Cheapest is to use a standard garden light string and run off the standard 12V transformer. Swap bulbs for LED versions, reduce from 60 w to 10 w overall.
                  or if a 200' extension cord costs more than $500, you can install solar, and run LED's right off the 12V battery. Several controllers have lighting functions, dusk - dawn. dusk +6 hours.....
                  Some low voltage LED;s are here https://www.wiredco.com/LED_Lighting...age_s/1874.htm
                  Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                  || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                  || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                  solar: http://tinyurl.com/LMR-Solar
                  gen: http://tinyurl.com/LMR-Lister

                  Comment


                  • #10
                    Originally posted by malborn View Post
                    In order to make it cheaper by using less solar controller amphere. should I desing it at 24 V ?
                    and can I do that by connecting two 12 solar panel in series and connecting 12 volt batteries in series ?
                    Is there anything else that I aware of ?

                    Thank you.
                    The key here is to use inexpensive Grid Tied Panels and a MPPT controlller, and YES you are on the right path. It takes a 300 watt PWM system to = a 200 watt MPPT system. MPPT controllers are much higher than PWM controllers of a given amperage. The issue is GGT panels are much higher voltage, thus you must use MPPT controllers.

                    Bu there eis the GOTCHA. A low voltage battery panel cost roughly 2 to 6 times more per watt than GT panels. You can buy GT panels for around $1 to $1.50/watt, and battery panels around $2 to $12/watt. So using the low end you can buy a single 200 watt GT panel for $200 plus a $200 20 amp MPPT controller for a total of $400. If you go the PWM route you need 2-150 watt Battery panels costing some $600 plus a $50 20 amp PWM controller for a total of around $650. That is a significant difference. However the expense does not end there. Two 150 watt paneels requires twice the wire and hardware a single 200 watt panel requires.

                    OK let's answer your question. A 20 amp MPPT controller like a Morningstar Sun Saver can input 200 watts @ 12 volt battery, and 400 watts @ 24 volt battery to deliver the same 15 amps. But what is not obvious is for each 12 volts of battery requires 18 volts of panel Vmp. All battery panels are rated 17 to 18 volts Vmp. GT panels are higher than that. A typical 200 watt GT panel has 50 cells with a 25 volt Vmp rating, so it could not be used on a 24 volt battery because the voltage is too low. Works just fine on a 12 volt battery.

                    So what do you do? Simple use a 72 cell panel with a Vmp of 36 volts, or you could use 2 battery panels wired in series. With the Sun Saver MPPT operating you do not have a lot of wiggle room at 24 volt battery with a max Voc voltage of 70 Voc aka Voltage Open Circuit. It can be a bit confusing using two terms Vmp and Voc, but it is really simple. For minimum use the panel Vmp spec and wheen added up is at least 34 to 36 Vmp on a 24 volt battery. On the maximum since you live in LA left coast, maximum is 70 Voc which is roughly about 56 Vmp.

                    Let's make it even easier for Dummies. Select you panels based on the number of cells in series. No less than 72, and no more than 90. Just remember if you wire the panels in series to add the cells. So if you use say battery panels which have 36 cells, two in series is 36 + 36 = 72 cells. Or two 45 cell GT panels in series is 45 + 45 = 90.

                    Hint GT panels come in 72 and 80 cells.
                    MSEE, PE

                    Comment


                    • #11
                      Be I read your very useful post and read some stuffs on web Thank you very much for very useful information and helping me


                      Consumption = 60 Watt x 11 hours x 1.5 (for MPPT) = [B]990 Watt.hours[/B]

                      I looked at the average solar radiation data from gaisma, the lowest sun hour for los angeles is about 2.59 hours

                      Size of Panel =( 990 Watt.hours/ 2,59 hours) = [B]382 Watts[/B]; --> 2 x 191 Watts Solar Panel in series

                      all losses =0,85
                      Dept of Discharge = 0,5
                      2.5 days reserve

                      Size of the Battery= 990 Watt.hours / (0,85 x 0,5 x 24 Volt ) x 2.5 days = [B]242 AH[/B] Battery ---> 2 x 121 AH battery 12 Volt in series

                      [B]pdf:[/B] http://www.amerescosolar.com/sites/d...G5SHP_DEKA.pdf

                      Size of Controller = (2 x 190 Watts / 24 Volt) X 1.2 (Safety factor) = [B]19 A[/B] solar controller

                      [B]Checkings[/B]

                      Solar Panel : Maximum power (Pmax) 190W 72 cells
                      Voltage at Pmax (Vmpp) 38.0V
                      Current at Pmax (Impp) 5.0A
                      Short circuit current (Isc) 5.5A
                      Open circuit voltage (Voc) 45.3V
                      [B]pdf: [/B]http://www.amerescosolar.com/sites/d...90J-190W_0.pdf

                      [B]Checking for Batteries[/B]

                      Because you said "12 volts of battery requires 18 volts of panel Vmp"
                      2 x 12 Volt batteries in series requires 2 x 18 = [B]36 Vmp[/B]
                      2 x 190 Watts Panels in series 2 x 38 = [B]76 Vmpp[/B] , so [B]*am I good to use it ?[/B]

                      [B]Checking for Solar Controller [/B]

                      Vpm (system) 2 x 38 Volt = [B]76 Volt[/B]
                      Voc (system) 2 x 45.3 Volt = [B]90.6 Volt [/B]


                      *[B]Which MPPT charger controller should we choose at 20 amps ? [/B]

                      [B]*Should I use fuses or diodes for this simple light?

                      the last question Why number of solar cell is important? 60 cell 100 watt solar panel is different than the 72 100 watt solar panel? [/B]


                      Thank you very much.




                      Comment


                      • #12
                        Originally posted by malborn View Post
                        Be I read your very useful post and read some stuffs on web Thank you very much for very useful information and helping me


                        Consumption = 60 Watt x 11 hours x 1.5 (for MPPT) = [B]990 Watt.hours[/B]

                        I looked at the average solar radiation data from gaisma, the lowest sun hour for los angeles is about 2.59 hours

                        Size of Panel =( 990 Watt.hours/ 2,59 hours) = [B]382 Watts[/B]; --> 2 x 191 Watts Solar Panel in series

                        all losses =0,85
                        Dept of Discharge = 0,5
                        2.5 days reserve

                        Size of the Battery= 990 Watt.hours / (0,85 x 0,5 x 24 Volt ) x 2.5 days = [B]242 AH[/B] Battery ---> 2 x 121 AH battery 12 Volt in series

                        [B]pdf:[/B] http://www.amerescosolar.com/sites/d...G5SHP_DEKA.pdf

                        Size of Controller = (2 x 190 Watts / 24 Volt) X 1.2 (Safety factor) = [B]19 A[/B] solar controller

                        [B]Checkings[/B]

                        Solar Panel : Maximum power (Pmax) 190W 72 cells
                        Voltage at Pmax (Vmpp) 38.0V
                        Current at Pmax (Impp) 5.0A
                        Short circuit current (Isc) 5.5A
                        Open circuit voltage (Voc) 45.3V
                        [B]pdf: [/B]http://www.amerescosolar.com/sites/d...90J-190W_0.pdf

                        [B]Checking for Batteries[/B]

                        Because you said "12 volts of battery requires 18 volts of panel Vmp"
                        2 x 12 Volt batteries in series requires 2 x 18 = [B]36 Vmp[/B]
                        2 x 190 Watts Panels in series 2 x 38 = [B]76 Vmpp[/B] , so [B]*am I good to use it ?[/B]

                        [B]Checking for Solar Controller [/B]

                        Vpm (system) 2 x 38 Volt = [B]76 Volt[/B]
                        Voc (system) 2 x 45.3 Volt = [B]90.6 Volt [/B]


                        *[B]Which MPPT charger controller should we choose at 20 amps ? [/B]
                        Close but no Cigar

                        Fist you are a little low on Insolation for LA. using latitude tilt 3.75 hours.

                        Battery First because it is easy peasy since we know 1Kwh/day.
                        12 volt = 1000wh x 5 /12 volts = [B]400 AH[/B]
                        24 volt = [B]200 AH[/B]
                        Close enough

                        Panel Wattage = 1000 wh x 1.5 / 3.75 = [B]400 watts[/B]

                        MPPT = 400w / 24 v = [B]17 amps[/B]
                        MPPT = 400w / 12 v = [B]35 amps[/B]


                        Originally posted by malborn View Post
                        Should I use fuses or diodes for this simple light?
                        No fuses between panels and controller. No diodes anywhere. Only fuses on battery term post will show you later what and where.

                        Originally posted by malborn View Post
                        the last question Why number of solar cell is important? 60 cell 100 watt solar panel is different than the 72 100 watt solar panel?
                        Cells determine the voltage.. For Voc 1 cell = roughly .61 volts, and Vmp = roughly .5 volt. Minimum Vmp for each 12 volt of battery is 18 volts or 36 cells. So for 24 volt you want a Vmp of at least 36 volts or 72 cells. With PWM controllers you must use 36 cell panels only. MPPT at least 36 or more. More is better to make efficiency higher and keeps cost down but there is a limit as you cannot exceed the MPPT controller max VOC input. That is an issue with small system as 15 to 20 amp controllers usually have a 70 Voc max. That means either 12 or 24 volt battery you are looking at around a max of 80 cells. There are a lot of 200 watt 72 and 80 cell panels for sale. Choose 80 if you get that option but no less than 72 if you intend to run 24 volt battery.
                        MSEE, PE

                        Comment


                        • #13
                          Thank you very much I understood clearly. I am very happy now I just have 2 question.

                          While you were calculating Panel Wattage and using 3,75 sun hours [B]([/B]1000 wh x 1.5 / 3.75 = [B]400 watts) [/B]you multiplied by 1,5 again. Where do it come from this 1.5 ? I think I already multiplied by 1.5 (For mppt) on consumption calculation ? [B]([/B]Consumption = 60 Watt x 11 hours x 1.5 (for MPPT) = [B]990 Watt.hours ) [/B]


                          I couldn't find Morningstar 20 Amp MPPT charge controller on their webpage. could you help me please to find it?

                          Could you suggest please any good book or source to desing solar ?

                          Comment


                          • #14
                            Originally posted by malborn View Post
                            While you were calculating Panel Wattage and using 3,75 sun hours [B]([/B]1000 wh x 1.5 / 3.75 = [B]400 watts) [/B]you multiplied by 1,5 again. Where do it come from this 1.5 ? I think I already multiplied by 1.5 (For mppt) on consumption calculation ? [B]([/B]Consumption = 60 Watt x 11 hours x 1.5 (for MPPT) = [B]990 Watt.hours ) [/B]
                            My bad. Did not read your opening statement. I thought 1 Kwh was your daily. Changes everything.

                            Panel Wattage = 825 x 1.5 / 3.25 = [B]380 watts[/B]. But no harm or foul using 400 watts
                            24 volt Battery = 825 x 5 / 24 volts = 172 AH
                            12 volt = 344 AH
                            MPPT = 380 / 24 = 15.8

                            If using the Morningstar Sun saver MPPT is 15 AMPS which works with 400 watts inpuut at 24 volt battery.

                            Bottom Line if I were you:

                            Panel - 400 watts
                            Battery = 24 Volts @ 200 AH
                            Morningstar Sunsaver MPPT 15 amp.

                            It is a perfect match made in heaven providing you got the daily watt hours right. December and January are the months you need to watch over. Spring, Summer, and Fall no worries. .

                            Solar 4 Dummies. [FONT=comic sans ms]There is no design book, its a secret.[/FONT]
                            MSEE, PE

                            Comment


                            • #15
                              I ordered the book from amazon Thank you very much. Almost done I have just 4 questions

                              1) Because we are going to use MPPT and 24 volt and you mentioned MPPT requires 72 cell solar panel, Should we use [B]72 cell + 72 cell= 144 cell[/B] solar panel or [B]36 cell + 36 cell =72 cell[/B] solar panel ?

                              2) I couldn't find 200 watt 72 cell 12 Volt solar panel to use? is it okay if our one solar panel 200 watt 24 volt 72 cells? [B]2 x (200 watt, 24 Volt,72 cells) = 400 Watts, 48 Volts,144 cells.[/B]

                              3) Is it a problem to connect [B]24 Volt [/B][B]60 watt led;[/B] [B]48 Volt panel[/B] and [B]24 volt battery bank[/B] to [B]15 amp mppt controller[/B]?

                              4) While we size controller [B]( [/B][B]380 / 24 volt = 15.8 amp )[/B] are we using [B]battery bank voltage[/B] or [B]solar panel voltage[/B] or [B]led lighting voltage[/B] ?

                              I am going to send picture of 60 w light when it is working on my garden

                              Comment

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